Prior art systems for assisted motion utilize exoskeletons, comprising rigid components (e.g., linkages) and joints (e.g., pin joint), attached to the user's body with the exoskeleton joint(s) being disposed to have an axis of rotation ideally collinear with a natural axis of rotation for adjacent joint(s). Exemplary prior art exoskeletons are shown in US Published Patent Application Nos. 2007/0123997 and 2011/0040216, both to Herr et al., and both of which are incorporated by reference herein in their entirety. Such rigid exoskeletons provide the ability to replace human movements that have been lost or severely compromised and are accordingly designed to enhance the user's stability, balance and safety. Other rigid exoskeletons serve as a platform to provide physical therapy sessions in a clinical environment, such as in a physical therapy clinic, or serve to assist able-bodied users to perform tasks more easily or for longer duration.
However, these rigid exoskeletons rely on rigid frameworks of linkages, coupled to the body at select locations via pads, straps, or other interface techniques. As the user flexes or extends their limbs, these rigid links move in parallel with the limb, adding considerable inertia to movement which must be overcome by motors or by the user. Though great effort has been made to reduce the weight and profile of these devices, they still cause considerable restriction to the user's motion and, in particular, add considerable impedance to the natural dynamics and kinematics of gait. This change to the normal kinematics of walking is one reason why these exoskeleton systems do not reduce the metabolic power required for locomotion. The rigid links also cause difficulty, particularly at the extremes of motion, because the pin-joints of the exoskeleton do not precisely match with the axes of the human joints, which move through intricate three dimensional paths. This causes misalignment of up to 10 cm during normal movement, causing pain and even injury to users. One solution has been to include redundant, passive degrees of freedom to allow the exoskeleton to travel and deform in key areas for wearer motion, however, this adds further weight to the systems.